It's not really required, but most hiring departments use them to filter out automated application processes, recruiters, and agencies. A cover letter should s

It's not really required, but most hiring departments use them to filter out automated application processes, recruiters, and agencies. A cover letter should show an individual's intent to work at a specific company, so it should add a step that's less automated to indicate that the applicant is a "real" direct applicant. Obviously there are ways around this, but that's one of the reasons people ask for cover letters. It's also an opportunity for an applicant to convince the hiring manager that they are a good candidate even if their resume may not clearly indicate that.